Air handling systems involve both outlet or distribution registers and return registers.
The air outlet registers are in many cases of relatively small dimension, typically being 4".times.10", and are usually located in walls or ceilings of a structure.
Return registers are, however, usually of much larger dimensions, in the region of for example 12".times.24", or 12".times.36". In most domestic construction for example the larger dimensions of the return registers are dictated by the manner in which the air distribution and return ducting is incorporated in the building structure. Distribution ducts are usually of relatively small dimensions, for example 4".times.10", and are led to every room in a dwelling. On the other hand, the return ducting is usually much larger, and the return registers will be located at only two or perhaps three different locations in the dwelling, usually in stairwells or in open rooms. The air return ducts are usually of much larger dimensions than the distribution ducts, because there are fewer air return registers and the same volume of air must be distributed, and returned, continuously.
The much larger size of the return ducts in many cases means that it is difficult to incorporate them in a typical dwelling wall, in which the thickness of the wall is only the thickness of the spacing provided by the studs provided in the wall.
Accordingly, it is common practice to provide air return ducts which are simply in the floor or beneath the basement floor joists. This form of duct is acceptable for return air purposes since the return air usually flows through door ways and stair wells, consequently eliminating the need for hot and cold air circulation in every room.
The return ducts may be in the region of 250 to 500 square inches for example depending upon the volumes of air being circulated.
Because of the location of the return ducts, it is usually necessary to have the return registers mounted on the floor.
As a result of this, it has been necessary in the past, to make floor registers of relatively heavy construction, such that they can bear the weight of persons walking about on the floor. Generally speaking this has been done in a simplified fashion by providing a criss-cross grid of metal strips. The strips running in one direction, usually the shorter direction, will be wider strips, and will be notched to receive and support the somewhat narrower strips running in the other direction.
In some cases, both transverse and longitudinal strips have been notched, somewhat in the fashion of an egg-crate.
A simple frame is provided around four sides of the register, in which the ends of the transverse and longitudinal strips are fastened. The edges of the frames are usually simply spot welded together.
These registers have been used for many years, and have proved more or less satisfactory, that is to say they provide a means of returning air and at the same time support the weight of persons walking on the floor.
However, as the price of steel increases, the cost of such registers increases, and becomes a significant factor. A typical floor register may weigh several pounds.
It is clearly desirable to reduce the amount of steel in such registers if possible, without losing the load bearing capacity.
A further factor in the design of such registers also occurs in the fact that persons will typically walk on them as part of the surface of the floor. Typically, persons walk about the floor in bare feet or stockinged feet. If the edges of the strips forming the register are sharp or burred, then it may cause cuts, or damage to clothing and the like.
In the past, it was common for such registers to be made with strips of steel formed with at least one edge which was subjected to a finishing and radiusing operation so as to avoid this problem. More recently, however, some manufacturers have neglected to do this additional operation to avoid increases in costs.
Clearly, it is desirable to take whatever steps can reasonably be taken to avoid this problem.
The construction of the frames in the past has involved a relatively costly method of holding the two corners of the frame together and spot welding them to a gusset plate. Any improvement that can be made in this operation without loss of rigidity, is to be desired.